Resource allocation method and device for supporting vehicle communication in next generation mobile communication system

ABSTRACT

Disclosed are: a communication technique for merging, with IOT technology, a 5G communication system for supporting a data transmission rate higher than that of a 4G system; and a system therefor. The present disclosure can be applied to intelligent services (for example, smart home, smart building, smart city, smart car or connected car, healthcare, digital education, retail, security, and safety-related services, and the like) based on 5G communication technology and IoT-related technology. A method of a terminal in a wireless communication system, according to the present invention, comprising: receiving system information including a V2X parameter; receiving a data packet based on the V2X parameter; and updating a state variable on the data packet when the data packet is related to a new service, wherein a sequence number included in the state variable is updated based on a sequence number of a data packet received for the first time.

TECHNICAL FIELD

The disclosure defines a service-specific resource pool to supportvarious vehicle-to-everything (V2X) services in a next-generation mobilecommunication system. In addition, the disclosure includes a method ofselecting a resource pool by an LTE terminal or an NR terminalsupporting V2X when a service-specific resource pool and aservice-agnostic resource pool coexist, and monitoring and datatransmission procedures accordingly.

In addition, the disclosure relates to a mobile communication systemand, more particularly, includes an overall process in the user plane ofa terminal supporting vehicle-to-everything (V2X) services newly definedin NR.

BACKGROUND ART

To meet the demand for wireless data traffic having increased sincedeployment of 4G communication systems, efforts have been made todevelop an improved 5G or pre-5G communication system. Therefore, the 5Gor pre-5G communication system is also called a “Beyond 4G Network” or a“Post LTE System”. The 5G communication system is considered to beimplemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, soas to accomplish higher data rates. To decrease propagation loss of theradio waves and increase the transmission distance, the beamforming,massive multiple-input multiple-output (MIMO), full dimensional MIMO(FD-MIMO), array antenna, an analog beam forming, large scale antennatechniques are discussed in 5G communication systems. In addition, in 5Gcommunication systems, development for system network improvement isunder way based on advanced small cells, cloud radio access networks(RANs), ultra-dense networks, device-to-device (D2D) communication,wireless backhaul, moving network, cooperative communication,coordinated multi-points (CoMP), reception-end interference cancellationand the like. In the 5G system, hybrid FSK and QAM modulation (FQAM) andsliding window superposition coding (SWSC) as an advanced codingmodulation (ACM), and filter bank multi carrier (FBMC), non-orthogonalmultiple access (NOMA), and sparse code multiple access (SCMA) as anadvanced access technology have also been developed.

The Internet, which is a human centered connectivity network wherehumans generate and consume information, is now evolving to the Internetof things (IoT) where distributed entities, such as things, exchange andprocess information without human intervention. The Internet ofeverything (IoE), which is a combination of the IoT technology and thebig data processing technology through connection with a cloud server,has emerged. As technology elements, such as “sensing technology”,“wired/wireless communication and network infrastructure”, “serviceinterface technology”, and “security technology” have been demanded forIoT implementation, a sensor network, a machine-to-machine (M2M)communication, machine type communication (MTC), and so forth have beenrecently researched. Such an IoT environment may provide intelligentInternet technology services that create a new value to human life bycollecting and analyzing data generated among connected things. IoT maybe applied to a variety of fields including smart home, smart building,smart city, smart car or connected cars, smart grid, health care, smartappliances and advanced medical services through convergence andcombination between existing information technology (IT) and variousindustrial applications.

In line with this, various attempts have been made to apply 5Gcommunication systems to IoT networks. For example, technologies such asa sensor network, machine type communication (MTC), andmachine-to-machine (M2M) communication may be implemented bybeamforming, MIMO, and array antennas. Application of a cloud radioaccess network (RAN) as the above-described big data processingtechnology may also be considered an example of convergence of the 5Gtechnology with the IoT technology.

Meanwhile, the need for a method for supporting vehicle-to-everything(V2X) services in a 5G communication system has emerged.

DESCRIPTION OF THE INVENTION Technical Problem

The disclosure is intended to support various vehicle-to-everything(V2X) services by defining a service-specific resource pool in anext-generation mobile communication system and designing the operationsof a terminal and a base station accordingly.

In addition, in order to satisfy the new requirements in NR apart fromthe V2X operation in the existing LTE, it is necessary to configure theoperation on the basic user plane required by introducing an upgradedscenario and NR V2X operation that satisfies the requirements. Theoperation on the user plane includes tasks such as MAC PDU formatdetermination, radio bearer management and initial configuration, andsecurity key configuration.

Solution to Problem

In order to solve the above problems, in a wireless communicationsystem, a method of a terminal according to the disclosure may include:receiving system information including V2X parameters; receiving a datapacket based on the V2X parameter; and updating a state variable for thedata packet if the data packet is related to a new service, wherein asequence number included in the state variable is updated based on thesequence number of the first received data packet.

In order to solve the above problems, in a wireless communicationsystem, a terminal according to the disclosure may include atransceiver; and a controller configured to: receive system informationincluding V2X parameters; receive a data packet based on the V2Xparameter; and update a state variable for the data packet if the datapacket is related to a new service, wherein a sequence number includedin the state variable is updated based on the sequence number of thefirst received data packet.

Advantageous Effects of Invention

According to an embodiment of the disclosure, a service-specificresource pool is defined to support various vehicle-to-everything (V2X)services in a next-generation mobile communication system. In addition,the disclosure proposes an overall operation method and device for theterminal and the base station, based on the service-specific resourcepool proposed above. Therefore, the base station can support various V2Xservices to the terminal by efficiently managing resources with lowsignaling overhead to the LTE terminal or NR terminal supporting V2Xservices, and the terminal can efficiently transmit and receive messagesaccording to the V2X service.

According to another embodiment of the disclosure, by specifyingfeatures on the user plane for supporting NR V2X services, it ispossible to clarify the operation of NR V2X and design to operate, basedon the NR system. Accordingly, it is possible to efficiently provide V2Xservices in the existing NR system.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a view illustrating a structure of an LTE system to which thedisclosure can be applied;

FIG. 1B is a view illustrating a radio protocol structure in an LTEsystem to which the disclosure can be applied;

FIG. 1C is a view illustrating the structure of a next-generation mobilecommunication system to which the disclosure can be applied;

FIG. 1D is a view illustrating a radio protocol structure of anext-generation mobile communication system to which the disclosure canbe applied;

FIG. 1E is a view illustrating V2X communication in a next-generationmobile communication system to which the disclosure is applied;

FIG. 1F is a view illustrating a procedure for monitoring andtransmitting data of a V2X terminal operating in mode 3 when aservice-specific resource pool and a service-agnostic resource poolcoexist in a next-generation mobile communication system;

FIG. 1G is a view illustrating a data transmission procedure of a V2Xterminal operating in mode 4 when a service-specific resource pool and aservice-agnostic resource pool coexist in a next-generation mobilecommunication system;

FIG. 1H is a view illustrating a block configuration of a terminalaccording to the disclosure;

FIG. 1I is a block diagram showing the configuration of a base stationaccording to the disclosure;

FIG. 2A is a view illustrating the structure of the LTE system of thedisclosure;

FIG. 2B is a view illustrating a radio protocol structure in the LTEsystem of the disclosure;

FIG. 2C is a view illustrating the structure of a next-generation mobilecommunication system to which the disclosure is applied;

FIG. 2D is a view illustrating a radio protocol structure of anext-generation mobile communication system to which the disclosure isapplied;

FIG. 2E is a view illustrating V2X communication within the cellularsystem of the disclosure;

FIG. 2F is a view illustrating a data transmission procedure of a V2Xterminal operating in mode 3 according to the disclosure;

FIG. 2G is a view illustrating a data transmission procedure of a V2Xterminal operating in mode 4 according to the disclosure;

FIG. 2H is a view illustrating a MAC PDU format applied to an NR V2Xsystem proposed in the disclosure;

FIG. 2I is a view illustrating sidelink radio bearer management,encryption, and decryption methods applied to the NR V2X system proposedin the disclosure;

FIG. 2J is a view illustrating an overall operation of transmitting andreceiving data in a user plane in the NR V2X system proposed by thedisclosure;

FIGS. 2KA and 2KB are views illustrating in detail a user plane radiobearer management and encryption operation of an NR V2X supportingterminal proposed in an embodiment of the disclosure;

FIG. 2L is a view illustrating a block configuration of a terminalaccording to an embodiment of the disclosure; and

FIG. 2M is a view illustrating a block configuration of a base stationaccording to an embodiment of the disclosure.

MODE FOR THE INVENTION First Embodiment

Hereinafter, the operation principle of the disclosure will be describedin detail in conjunction with the accompanying drawings. In thefollowing description of the disclosure, a detailed description of knownfunctions or configurations incorporated herein will be omitted when itmay make the subject matter of the disclosure unnecessarily unclear. Theterms which will be described below are terms defined in considerationof the functions in the disclosure, and may be different according tousers, intentions of the users, or customs. Therefore, the definitionsof the terms should be made based on the contents throughout thespecification.

In the following description of the disclosure, a detailed descriptionof known functions or configurations incorporated herein will be omittedwhen it may make the subject matter of the disclosure unnecessarilyunclear. Hereinafter, embodiments of the disclosure will be describedwith reference to the accompanying drawings.

In the following description, terms for identifying access nodes, termsreferring to network entities, terms referring to messages, termsreferring to interfaces between network entities, terms referring tovarious identification information, and the like are illustratively usedfor the sake of convenience. Therefore, the disclosure is not limited bythe terms as used below, and other terms referring to subjects havingequivalent technical meanings may be used.

In the following description, the disclosure uses terms and namesdefined in 3rd generation partnership project long term evolution (3GPPLTE) standards for the convenience of description. However, thedisclosure is not limited by these terms and names, and may be appliedin the same way to systems that conform other standards. In thedisclosure, the term “eNB” may be interchangeably used with the term“gNB” for the convenience of description. That is, a base stationdescribed as “eNB” may indicate “gNB”.

FIG. 1A is a view illustrating a structure of an LTE system to which thedisclosure can be applied.

Referring to FIG. 1A, as illustrated, a radio access network of the LTEsystem may include evolved node Bs (hereinafter referred to as ENB, NodeB, or base station) 1 a-05, 1 a-10, 1 a-15, and 1 a-20, a mobilitymanagement entity (MME) 1 a-25, and a serving-gateway (S-GW) 1 a-30. Auser equipment (hereinafter, referred to as “UE” or “terminal”) 1 a-35may access an external network through the ENB 1 a-05 1 a-20 and theS-GW 1 a-30.

In FIG. 1A, the ENBs 1 a-05 to 1 a-20 correspond to the existing node Bof the UMTS system. The ENB is connected to the UEs 1 a-35 through aradio channel and performs a more complex role than the existing node B.In the LTE system, all user traffic, including real-time services suchas voice over IP (VoIP) through the Internet protocol, are servicedthrough a shared channel, a device for scheduling by collecting stateinformation such as buffer status, available transmission power status,and channel status of UEs is required, and ENBs 1 a-05 to 1 a-20 are incharge of the device. One ENB typically controls multiple cells. Forexample, in order to implement a transmission rate of 100 Mbps, the LTEsystem uses an orthogonal frequency division multiplexing (OFDM) as aradio access technology in, for example, a 20 MHz bandwidth. Inaddition, an adaptive modulation & coding (hereinafter, referred to as“AMC”) scheme is applied to determine a modulation scheme and a channelcoding rate according to a channel state of the terminal.

The S-GW 1 a-30 is a device that provides a data bearer, and generatesor removes a data bearer under the control of the MME 1 a-25. The MME isa device responsible for various control functions as well as mobilitymanagement functions for a terminal, and is connected to a plurality ofbase stations.

FIG. 1B is a view illustrating a radio protocol structure in an LTEsystem to which the disclosure can be applied.

Referring to FIG. 1B, the radio protocol of the LTE system is composedof a packet data convergence protocols (PDCP) 1 b-05, 1 b-40, a radiolink control (RLC) 1 b-10, 1 b-35, and a medium access control (MAC) 1b-15, 1 b-30, in the terminal and eNB, respectively.

Packet data convergence protocols (PDCPs) 1 b-05 and 1 b-40 are incharge of operations such as IP header compression/restore. The mainfunctions of PDCP are summarized as follows.

-   -   Header compression and decompression: ROHC only    -   Transfer of user data    -   In-sequence delivery of upper layer PDUs at PDCP        re-establishment procedure for RLC AM    -   For split bearers in DC (only support for RLC AM): PDCP PDU        routing for transmission and PDCP PDU reordering for reception    -   Duplicate detection of lower layer SDUs at PDCP re-establishment        procedure for RLC AM    -   Retransmission of PDCP SDUs at handover and, for split bearers        in DC, of PDCP PDUs at PDCP data-recovery procedure, for RLC AM    -   Ciphering and deciphering    -   Timer-based SDU discard in uplink

The radio link controls (RLCs) 1 b-10 and 1 b-35 reconstruct a PDCPpacket data unit (PDU) to an appropriate size and performs an ARQoperation. The main functions of RLC are summarized as follows.

-   -   Transfer of upper layer PDUs    -   Error Correction through ARQ (only for AM data transfer)    -   Concatenation, segmentation, and reassembly of RLC SDUs (only        for UM and AM data transfer)    -   Re-segmentation of RLC data PDUs (only for AM data transfer)    -   Reordering of RLC data PDUs (only for UM and AM data transfer)    -   Duplicate detection (only for UM and AM data transfer)    -   Protocol error detection (only for AM data transfer)    -   RLC SDU discard (only for UM and AM data transfer)    -   RLC re-establishment

The MACs 1 b-15 and 1 b-30 are connected to several RLC layer entitiesconfigured in one UE, and perform an operation of multiplexing RLC PDUsto MAC PDUs and demultiplexing RLC PDUs from MAC PDUs. The mainfunctions of MAC are summarized as follows.

-   -   Mapping between logical channels and transport channels    -   Multiplexing/demultiplexing of MAC SDUs belonging to one or        different logical channels into/from transport blocks (TB)        delivered to/from the physical layer on transport channels    -   Scheduling information reporting    -   Error correction through HARQ    -   Priority handling between logical channels of one UE    -   Priority handling between UEs by means of dynamic scheduling    -   MBMS service identification    -   Transport format selection    -   Padding

The physical layers 1 b-20 and 1 b-25 channel-code and modulate upperlayer data, convert the same into OFDM symbols, and transmit the same tothe radio channel, or demodulate OFDM symbols received through the radiochannel, decode the channel, and deliver the same to the upper layer.

FIG. 1C is a view illustrating the structure of a next-generation mobilecommunication system to which the disclosure can be applied;

Referring to FIG. 1 c , as illustrated, the radio access network of thenext-generation mobile communication system (hereinafter, referred to as“NR” or “5G”) includes a next-generation base station (new radio node B,hereinafter referred to as “NR gNB” or “NR base station”) 1 c-10 and newradio core network (NR CN) 1 c-05. The user equipment (new radio userequipment, hereinafter, referred to as “NR UE” or “terminal”) 1 c-15accesses an external network through the NR gNB 1 c-10 and NR CN 1 c-05.

In FIG. 1C, the NR gNB 1 c-10 corresponds to the eNB of the existing LTEsystem. The NR gNB is connected to the NR UE 1 c-15 through a radiochannel and can provide a service superior to that of the existing NodeB. In the next-generation mobile communication system, all user trafficis serviced through a shared channel, so a device that collects andschedules status information such as buffer status, availabletransmission power status, and channel status of UEs is required, andthe NR NB 1 c-10 is in charge.

One NR gNB typically controls multiple cells. In order to implementultra-high-speed data transmission compared to the current LTE, it canhave more than the existing maximum bandwidth, and a beamformingtechnology may be additionally grafted using orthogonal frequencydivision multiplexing (OFDM) as a wireless access technology. Inaddition, an adaptive modulation coding (AMC) method is applied todetermine a modulation scheme and a channel coding rate according to achannel state of the terminal.

The NR CN 1 c-05 performs functions such as mobility support, bearerconfiguration, and QoS configuration. The NR CN is a device responsiblefor various control functions as well as mobility management functionsfor a terminal, and is connected to a plurality of base stations. Inaddition, the next-generation mobile communication system can beinterlocked with the existing LTE system, and the NR CN is connected tothe MME 1 c-25 through a network interface. The MME is connected to theexisting eNB 1 c-30.

FIG. 1D is a view illustrating a radio protocol structure of anext-generation mobile communication system to which the disclosure canbe applied.

Referring to FIG. 1D, the radio protocol of the next-generation mobilecommunication system is composed of an NR PDCP 1 d-05, 1 d-40, an NR RLC1 d-10, 1 d-35, an NR MAC 1 d-15, 1 d-30 in the terminal and the NR basestation, respectively. The main functions of the NR PDCPs 1 d-05, 1 d-40may include some of the following functions.

-   -   Header compression and decompression: ROHC only    -   Transfer of user data    -   In-sequence delivery of upper layer PDUs    -   Out-of-sequence delivery of upper layer PDUs    -   PDCP PDU reordering for reception    -   Duplicate detection of lower layer SDUs    -   Retransmission of PDCP SDUs    -   Ciphering and deciphering    -   Timer-based SDU discard in uplink

In the above, the reordering function of the NR PDCP device refers to afunction of reordering PDCP PDUs received from a lower layer in orderbased on a PDCP sequence number (SN), and may include a function ofdelivering data to an upper layer in a reordered order, may include afunction of immediately delivering data without considering the order,may include a function of reordering the order and recording the lostPDCP PDUs, may include a function to report the status of the lost PDCPPDUs to the transmitting side, and may include a function to requestretransmission of the lost PDCP PDUs.

The main functions of the NR RLCs 1 d-10, 1 d-35 may include some of thefollowing functions.

-   -   Transfer of upper layer PDUs    -   In-sequence delivery of upper layer PDUs    -   Out-of-sequence delivery of upper layer PDUs    -   Error Correction through ARQ    -   Concatenation, segmentation and reassembly of RLC SDUs    -   Re-segmentation of RLC data PDUs    -   Reordering of RLC data PDUs    -   Duplicate detection    -   Protocol error detection    -   RLC SDU discard    -   RLC re-establishment

In the above, the in-sequence delivery function of the NR RLC devicerefers to a function of sequentially delivering RLC SDUs received from alower layer to an upper layer, and may include a function ofreassembling and delivering when one RLC SDU is originally divided intomultiple RLC SDUs and received, may include a function of rearrangingthe received RLC PDUs based on an RLC sequence number (SN) or a PDCPsequence number (SN), may include a function of reordering the order torecord lost RLC PDUs, may include a function of reporting the status oflost RLC PDUs to the transmitting side, may include a function ofrequesting retransmission of lost RLC PDUs, may include a function ofsequentially delivering only RLC SDUs prior to the lost RLC SDU to anupper layer when there is a lost RLC SDU, may include a function ofsequentially delivering all RLC SDUs received before the timer starts toan upper layer if a predetermined timer expires even if there is a lostRLC SDU, or may include a function of sequentially delivering all RLCSDUs received so far to an upper layer if a predetermined timer expireseven if there is a lost RLC SDU. In addition, the RLC PDUs may beprocessed in the order of reception (regardless of the order of serialnumber and sequence number, in the order of arrival) and delivered tothe PDCP device regardless of the order (out-of-sequence delivery), andin the case of a segment, segments stored in a buffer or to be receivedin the future may be received, reconstructed into one complete RLC PDU,processed, and delivered to the PDCP device. The NR RLC layer may notinclude a concatenation function, and the function may be performed inthe NR MAC layer or may be replaced by a multiplexing function of the NRMAC layer.

In the above, the out-of-sequence delivery function of the NR RLC devicerefers to a function of directly delivering RLC SDUs received from alower layer to an upper layer regardless of order, and may include afunction of reassembling and delivering when one RLC SDU is originallydivided into multiple RLC SDUs and received, and may include a functionof storing the RLC SNs or PDCP SNs of received RLC PDUs, sorting theorder, and recording the lost RLC PDUs.

The NR MACs 1 d-15 and 1 d-30 may be connected to several NR RLC layerentities configured in one terminal, and the main functions of the NRMAC may include some of the following functions.

-   -   Mapping between logical channels and transport channels    -   Multiplexing/demultiplexing of MAC SDUs    -   Scheduling information reporting    -   error correction through HARQ    -   Priority handling between logical channels of one UE    -   Priority handling between UEs by means of dynamic scheduling    -   MBMS service identification    -   Transport format selection    -   Padding

The NR PHY layers 1 d-20, 1 d-25 may channel-code and modulate upperlayer data, convert the same into OFDM symbols, and transmit the same tothe radio channel, or demodulate and channel-decode OFDM symbolsreceived through the radio channel and transmit the same to the upperlayer.

In the disclosure, a service-specific resource pool is defined tosupport various vehicle-to-everything (V2X) services in anext-generation mobile communication system. In particular, innext-generation mobile communication systems, since requirements arevery different according to usage cases, the service-specific resourcepool is defined in the serving cell and inter-frequency to supportvarious V2X services. In addition, the disclosure proposes a method foran LTE terminal or an NR terminal supporting V2X services to select aresource pool when a service-specific resource pool and aservice-agnostic resource pool proposed above coexist, and proposes amonitoring and data transmission procedure according to the method.

Table 1 shows the classification of the type, range, and data rate foreach V2X service in the next generation mobile communication system towhich the disclosure is applied.

Referring to Table 1, unlike the existing LTE systems (releases 14/15V2X), which support only uniform V2X services such as low data rate suchas basic safety message (BSM), cooperative awareness message (CAM),decentralized environmental notification message (DENM), one-way P2Xservice, etc., wide communication or transmission range, and publicservices, the next-generation mobile communication systems are expectedto support various data rates, communication and transmission areas, andpublic or private services due to the introduction of new services suchas advanced driving, extended sensor, and platooning. Accordingly, thedisclosure proposes a method of classifying V2X services as shown inTable 1 below, based on the requirements and use cases for each service.The table proposed as follows refers to 3GPP standard TR 22.886 “Studyon enhancement of 3GPP Support for 5G V2X services”.

TABLE 1 Type Range Data Rate Usage Rel-14/-15 Public High Low BSM, CAM,V2X DENM, P2X Advanced Public Medium Medium Information Driving sharingfor automated driving, Intersection safety information, Copperative lanechange, etc Extended Public Low (adjacent High Sensor cars) PlatooningPrivate/ Medium: Medium Public Leader −> follower, follower −> leaderLow: follower <−> follower

FIG. 1E is a view illustrating V2X communication in a next-generationmobile communication system to which the disclosure is applied.

V2X collectively refers to communication technology through allinterfaces with the vehicle, and may include vehicle-to-vehicle (V2V),vehicle-to-infrastructure (V2I), vehicle-to-pedestrian (V2P),vehicle-to-network (V2N), and the like, according to the shape andcommunication components. The V2P and V2V basically follow the structureand operation principle of Rel-13 device-to-device (D2D).

The base station 1 e-01 may communicate with at least one vehicleterminal 1 e-05, 1 e-10 and a pedestrian portable terminal 1 e-15located in the cell 1 e-02 supporting V2X. For example, the vehicleterminal 1 e-05 may perform cellular communication with the base station1 e-01 using the vehicle terminal-base station link (Uu) 1 e-30, 1 e-35,and the vehicle terminal 1 e-05 may perform device-to-device (D2D) usinga side link PC5 1 e-20, 1 e-25 with another vehicle terminal 1 e-10 or apedestrian portable terminal 1 e-15.

In order for the vehicle terminal 1 e-05 and another vehicle 1 e-10, orthe vehicle terminals 1 e-05 and 1 e-10 and the pedestrian mobileterminal 5 c-15 to directly transmit and receive information by usingthe sidelinks 1 e-20 and 1 e-25, the base station needs to allocate aresource pool that can be used for sidelink communication. According tohow the base station allocates resources to the terminal, the allocationcan be divided into scheduled resource allocation (mode 3) and UEautonomous resource allocation (mode 4).

The scheduled resource allocation is a method in which the base stationallocates resources used for sidelink transmission to RRC-connectedterminals in a dedicated scheduling scheme. The above method iseffective for interference management and resource pool management(dynamic allocation, semi-persistence transmission) because the basestation can manage the resources of the sidelink. In addition, in thecase of scheduled resource allocation (mode 3) in which the base stationallocates and manages resources for V2X, when the RRC connected terminalhas data to be transmitted to other terminals, the terminal may requestresource allocation from the base station using an RRC message or a MACcontrol element (hereinafter, referred to as “CE”). Here, the RRCmessage may be a SidelinkUEInformation or UEAssistanceInformationmessage. Meanwhile, the MAC CE may, as an example, be a buffer statusreport MAC CE of a new format (including at least an indicatorindicating that a buffer status report for V2P communication andinformation on the size of data buffered for D2D communication). Fordetailed format and contents of the buffer status report used in 3GPP,refer to 3GPP standard TS36.321 “E-UTRA MAC Protocol Specification”.

On the other hand, the UE autonomous resource allocation is a method inwhich a base station provides a sidelink transmission/reception resourcepool for V2X to the terminal as system information, and the terminalselects a resource pool according to a predetermined rule. The resourceselection method may include zone mapping, sensing-based resourceselection, and random selection, regardless of service or service type.

The structure of the resource pool for V2X may be configured in a mannerin which resources 1 e-40, 1 e-50, 1 e-60 for scheduling allocation (SA)and resources 1 e-45, 1 e-55, 1 e-65 for data transmission are adjacentto each other to form one subchannel, or resources 1 e-70, 1 e-75, 1e-80 for SA and resources 1 e-85, 1 e-90, 1 e-95 for data transmissionare not adjacent. Regardless of which of the above two structures isused, the resource for the SA is composed of two consecutive PRBs andincludes information indicating the location of the resource fortransmitting data. The number of terminals receiving the V2X service inone cell may be multiple, and the relationship between the base station1 e-01 and the terminals 1 e-05, 1 e-10, and 1 e-15 described above canbe extended and applied.

FIG. 1F is a view illustrating a procedure for monitoring andtransmitting data of a V2X terminal operating in mode 3 when aservice-specific resource pool and a service-agnostic resource poolcoexist in a next-generation mobile communication system.

Referring to FIG. 1F, an application server (hereinafter, V2Xapplication server) 1 f-05 provides parameter information of V2Xcommunication to terminals 1 f-01, 1 f-02 (1 f-10). Alternatively, thecontrol function (hereinafter, V2X control function) (1 f-04) mayreceive parameter information from the V2X application server 1 f-05 andprovide parameter information for V2X communication to the terminals 1f-01, 1 f-02 (1 f-10).

The provisioned parameter may include mapping information of V2Xservices and destination layer-2 ID(s). For example, since thenext-generation mobile communication system should support new V2Xservices such as platooning, advanced driving, extended sensors, etc.must be supported, new V2X services may be mapped to a destinationlayer-2 ID(s) through an identifier such as a provider serviceidentifier (PSID), intelligent transport system-application identifiers(ITS-AIDs), or new identifiers of a V2X application.

In addition, the provisioned parameters may include mapping informationof V2X frequencies (hereinafter, V2X frequencies) and V2X services, orV2X frequencies and V2X service types (e.g., PSIDs or ITS-AIDs or newidentifiers specified above), or V2X frequencies and radio accesstechnology (RAT). Here, the V2X frequencies may represent the V2X LTEfrequency or the V2X NR frequency or both, and thus the radio accesstechnology may also represent E-UTRA or NR or both.

In addition, the mapping information specified above may additionallyinclude information on a geographic area(s). For example, in a specificgeographic area, the V2X frequencies may not be available due to localregulations, and in a geographic area where privacy is sensitive, thelist of available V2X services or the V2X service types may bedifferent, so information on the geographic area may be included in theprovisioned parameter together.

In addition, the provisioned parameter may include mapping informationof a V2X service and a communication range or a transmission range.

In addition, the provisioned parameters may include mapping informationon prose per-packet priority (PPPP) and packet delay budget, or mappinginformation of V2X service and PPPP, or mapping information of V2Xservice and prose per-packet reliability (PPPR) for V2X communication.

The provisioned parameter may include all of the information describedabove or at least one of the information described above.

The terminals 1 f-01 and 1 f-02 pre-configure parameters initiallyprovided from the V2X application server 1 f-05 or the V2X controlfunction 1 f-04.

If the terminal 1 f-01 having previously configured parameters above isinterested in a specific V2X service x, the terminal searches for asuitable cell to camp-on by performing a selection or a selectionprocedure. In addition, the terminal 1 f-01 camps on the cell (1 f-15).In this case, the terminal may find a cell to camp-on at a V2X frequencysupported by a home public land mobile network (HPLMN) mapped with aspecific V2X service x. The terminal 1 f-01 camping on the cell canreceive (1 f-20) SIB21 from the base station 1 f-03.

The system information (1 f-20) may include at least one of informationon the service-specific resource pools at a serving frequency for signaltransmission and reception and information on the service-agnosticresource pools, information on service-specific resource pools ofinter-frequency and information on service-agnostic resource pools,information on service-specific resource pools of inter-RAT andinformation on service-agnostic resource pools, information forconfiguring synchronization, zone configuration information for theterminal to autonomously select a resource and transmit data, andpriority configuration information of a sidelink (PC5) and an LTE/NRuplink and downlink (Uu).

The information on the service-specific resource pool may specificallyinclude information about radio access technology (E-UTRA or NR) thatcan be supported in the resource pool for each service, information onthe mapped services (e.g., a list of V2X services mapped with acombination of a communication region, a transport region, PPPP, PPPR,and Destination Layer-2 ID(s)), resource pool configuration information(e.g., time-domain resource in bitmap format, frequency-domain resource,subcarrier spacing information or cyclic prefix length when NR issupported), transmission power configuration information including amaximum allowed transmission power, and configuration information for asensing operation.

The information on the service-agnostic resource pool does not includeinformation on mapped services, and may include information on the radioaccess technology specified above, resource pool configurationinformation, transmission power configuration information, andconfiguration information for sensing operation.

The terminal 1 f-01 receiving the system information may determine thefrequencies/RATs monitored for V2X communication (1 f-25). In this case,the terminal may determine the frequencies/RATs to be monitored based ona set of two categories.

The first set (1st set of the monitoring frequencies/RATs, or firstresource set) may include an intersection of frequencies specified tosupport V2X in system information or RRC message (e.g., RRC ConnectionReconfiguration message) and frequencies mapped with V2X servicesconsidered by the terminal.

The second set (2nd set of the monitoring frequencies/RATs, or secondresource set) may include intra-RAT frequencies/inter-RAT frequenciesproviding a service-specific resource pool to support a specific V2Xservice x.

The terminal first monitors the second set of resource pools for eachservice. If there is no frequencies supporting a specific V2X service xin the resource pool for each service, the terminal monitors theresource pool irrelevant to the service included in the first set.

When data traffic for a specific V2X service x is generated (1 f-30),the terminal performs an RRC connection with the base station (1 f-35).In the above RRC connection process, the terminal may transmit an RRCmessage by adding information on a specific V2X service x to the basestation. The RRC connection process may be performed before data trafficfor a specific V2X service x is generated (1 f-30).

When there is a service-specific resource pool that supports a specificV2X service x in the serving frequency, the terminal 1 1 f-01 requeststhe base station 1 f-03 for transmission resources for V2X communicationwith other terminals 1 f-02 or base station 1 f-03 using theservice-specific resource pool (1 f-40). In this case, the terminal mayrequest transmission resources using an RRC message or a MAC controlelement (CE).

Here, as the RRC message, SidelinkUEInformation orUEAssistanceInformation message may be used. Meanwhile, the MAC CE maybe, as an example, a buffer status report MAC CE of a new format(including at least an indicator indicating that a buffer status reportfor V2X communication and information on the size of data buffered forD2D communication).

The base station 1 f-03 may allocate the V2X transmission resource tothe terminal 1 (1 f-01) (1 f-45). The base station 1 f-03 may allocateV2X transmission resources through a dedicated RRC message, and themessage may be included in the RRCConnectionReconfiguration message.

The resource allocation may be a V2X resource scheduled from the basestation through the Uu interface according to the type of trafficrequested by the terminal, congestion of the link, or V2X service, ormay be a resource directly selected by the terminal from the resourcepool provided from the base station (resource for PC5). In order todetermine the resource allocation, the terminal may add and transmitPPPP or PPPR or LCID information of V2X traffic throughUEAssistanceInformation or MAC CE. Since the base station also knowsinformation on the resources used by other terminals, the base stationschedules a resource requested by the terminal 1 among remainingresources.

In addition, when the RRC message (RRCconnection reconfigurationmessage) includes SPS configuration information through Uu, the basestation may activate the SPS by transmitting DCI through the PDCCH (1f-50).

The terminal 1 1 f-01 may select a transmission link and resourceaccording to the resource and transmission method allocated from thebase station 1 f-03 (1 f-55), and transmit data to the terminals 1 f-02or to the base station 1 f-03 (1 f-60).

If there is no service-specific resource pool that supports a specificV2X service x in the serving frequency, but there is a service-specificresource pool that supports a specific V2X service x in the non-servingfrequency, the terminal 1 1 f-01 requests a transmission resourcecapable of V2X communication with other terminals 1 f-02 or base station1 f-03 from the base station 1 f-03 (1 f-40). In this case, the terminalmay request a transmission resource using an RRC message or MAC CE.

Here, the RRC message may be a SidelinkUEInformation orUEAssistanceInformation message. Meanwhile, the MAC CE may be, as anexample, a buffer status report MAC CE of a new format (including atleast an indicator indicating that a buffer status report for V2Xcommunication and information on the size of data buffered for D2Dcommunication).

The base station 1 f-03 may allocate a V2X transmission resource to theterminal 1 1 f-01 (1 f-45). The base station 1 f-03 may allocate V2Xtransmission resources through a dedicated RRC message, and the messagemay be included in the RRCConnectionReconfiguration message.

The resource allocation may be a V2X resource scheduled from the basestation through the Uu interface according to the type of trafficrequested by the terminal, congestion of the link, or V2X service, ormay be a resource directly selected by the terminal from the resourcepool provided from the base station (resource for PC5). In order todetermine the resource allocation, the terminal may add and transmitPPPP or PPPR or LCID information of V2X traffic throughUEAssistanceInformation or MAC CE. Since the base station also knowsinformation on the resources used by other terminals, the base stationmay schedule a resource requested by the terminal 1 among remainingresources.

In addition, when the RRC message (RRCconnection reconfigurationmessage) includes SPS configuration information through Uu, the basestation may activate the SPS by transmitting DCI through the PDCCH (1f-50). Terminal 1 1 f-01 may select a transmission link and resourceaccording to the resource and transmission method allocated from thebase station 1 f-03 (1 f-55), and transmit data to the terminals 1 f-02or to the base station 1 f-03 (1 f-60).

FIG. 1G is a view illustrating a data transmission procedure of a V2Xterminal operating in mode 4 when a service-specific resource pool and aservice-agnostic resource pool coexist in a next-generation mobilecommunication system.

Referring to FIG. 1G, a V2X application server 1 g-05 may provideparameter information for V2X communication to the terminals 1 g-01 and1 g-02 (parameter provisioning) (1 g-10). Alternatively, the V2X controlfunction (1 g-04) may receive parameter information from the V2XApplication Server 1 g-05 and provide parameter information for V2Xcommunication to the terminals 1 g-01, 1 g-02 (1 g-10).

The provisioned parameter may include mapping information of V2Xservices and destination layer-2 ID(s). For example, in anext-generation mobile communication system, new V2X services such asplatooning, advanced driving, extended sensors, etc. should besupported. Therefore, the new V2X service may be mapped to thedestination layer-2 ID(s) through an identifier such as PSID or ITS-AIDsor new identifiers of the V2X application.

In addition, the provisioned parameters may include mapping informationof V2X frequencies and V2X services or V2X frequencies and V2X servicetypes (e.g., PSID or ITS-AIDs or new identifiers specified above) or V2Xfrequencies and radio access technology (RAT). Here, the V2X frequenciesmay represent the V2X LTE frequency or the V2X NR frequency or both, andthus the radio access technology may also represent E-UTRA or NR orboth.

In addition, the mapping information specified above may additionallyinclude information on a geographic area(s). For example, in a specificgeographic area, the usage of the V2X frequencies may not be possibledue to local regulations, and in a geographic area where privacy issensitive, the list of available V2X services or the V2X service typemay be different, thus, information on the geographic area may beincluded in the provisioned parameters together.

In addition, the provisioned parameter may include mapping informationof a V2X service and a communication range or a transmission range.

In addition, the provisioned parameters may include mapping informationof PPPP and packet delay budget, mapping information of V2X service andPPPP, or mapping information of V2X service and PPPR for V2Xcommunication.

The provisioned parameter may include all of the information describedabove or at least one of the information described above.

The terminals 1 g-01 and 1 g-02 may pre-configure parameters initiallyprovided from the V2X application server 1 g-05 or the V2X controlfunction 1 f-04.

There is a difference in that, unlike mode 3, in which the base station1 g-03 is directly involved in resource allocation, in mode 4 operation,the terminal 1 1 g-01 may autonomously select resources and transmitdata, based on the resource pool previously received through systeminformation.

The disclosure proposes that the base station 1 g-03 in V2Xcommunication allocates a sidelink service-specific resource pool and asidelink service-agnostic resource pool for terminal 1 1 g-01. Aterminal interested in a specific V2X service x may autonomously selectan available resource pool after sensing resources used by otherneighboring terminals from the sidelink resource pool for each service.Alternatively, the terminal may randomly select a resource from apreconfigured resource pool.

In addition, a terminal that intends to transmit/receive informationirrelevant to a service type may autonomously select an availableresource pool after sensing resources used by other neighboringterminals from the sidelink service-agnostic resource pool.Alternatively, the terminal may randomly select a resource from apreconfigured resource pool.

The terminal 1 1 g-01 having preconfigured parameters above may performa selection or selection procedure when interested in a specific V2Xservice x to find a suitable cell for camp-on. Then, the terminal 1 g-01camps on the cell (1 g-15). Here, the terminal may find a cell tocamp-on to a V2X frequency supported by the HPLMN mapped to a specificV2X service x. The terminal 1 1 g-01 camping on may receive (1 g-20)SIB21 from the base station 1 g-03.

The system information (1 g-20) may include at least one of informationon a service-specific resource pool in a serving frequency for signaltransmission and reception, information on a service-agnostic resourcepool, information on service-specific resource pool and information onservice-agnostic resource pool of inter-frequency, information on aservice-agnostic resource pool, information on a service-specificresource pool and information on a service-agnostic resource pool ofinter-RAT, information for configuring synchronization, zoneconfiguration information for the terminal to autonomously selectresources and transmit data, priority configuration information of thesidelink (PC5) and LTE/NR uplink and downlink (Uu)

The information on service-specific resource pool may specificallyinclude information about radio access technology (E-UTRA or NR) thatcan be supported in the resource pool for each service, information onthe mapped services (e.g., a list of V2X services mapped with acombination of a communication region, a transport region, PPPP, PPPR,and Destination Layer-2 ID(s)), resource pool configuration information(e.g., time-domain resource in bitmap format, frequency-domain resource,subcarrier spacing information or cyclic prefix length when NR issupported), transmission power configuration information including amaximum allowed transmission power, and configuration information for asensing operation.

The information on service-agnostic resource pool does not includeinformation on mapped services, and may include information on the radioaccess technology specified above, resource pool configurationinformation, transmission power configuration information, andconfiguration information for sensing operation.

The terminal 1 1 g-01 receiving the system information may determine thefrequencies/RATs monitored for V2X communication (1 g-25). In this case,the terminal 1 1 g-01 may determine the monitored frequencies/RATs,based on a set of two categories.

The first set (1st set of the monitoring frequencies/RATs, or firstresource set) may include an intersection of frequencies specified tosupport V2X in system information or RRC message (e.g., RRC ConnectionReconfiguration message) and frequencies mapped with V2X servicesconsidered by the terminal.

The second set (2nd set of the monitoring frequencies/RATs, or secondresource set) may include intra-RAT frequencies/inter-RAT frequenciesproviding a service-specific resource pool to support a specific V2Xservice x.

The terminal first monitors the second set of resource pools for eachservice. If there is no frequencies supporting a specific V2X service xin the resource pool for each service, the terminal monitors theresource pool irrelevant to the service included in the first set. Ifthe terminal 1 1 g-01 does not receive the system information or the RRCmessage, the terminal may perform the above operation, based onpreconfigured information from the V2X control function 1 g-04 or V2Vapplication server 1 g-05.

When data traffic for a specific V2X service x is generated (1 g-30),the terminal 1 1 g-01 may select a resource in the time/frequency domain(1 g-35) and transmit data to at least one other terminal 1 g-02according to the configuration information (e.g., transmission operation(one dynamic allocation transmission, dynamic allocation multipletransmission, one sensing-based transmission, sensing-based multipletransmission, random transmission) configured for a service-specificresource pool for a specific V2X service x) received from the basestation 1 g-03 through system information (1 g-40).

In a mode 4 operation, for sensing-based multi-transmission, theterminal may sense resources for transmitting signals from otherterminals, select a transmittable resource block from the resource poolin which the corresponding transmission is performed, and then reserveresources to be periodically transmitted. Thereafter, if the data packetgenerated by the terminal is changed or disappears, the terminalrestarts or cancels the above sensing and resource reservation operationso that a new data packet can be delivered.

As described above, sensing and resource reservation-basedmulti-transmission may be basically operated, and if the sensingoperation is not well performed, communication may be performed throughrandom resource selection from a corresponding resource pool. If theterminal does not receive system information or RRC message, the aboveoperation is performed based on preconfigured information from a V2Xcontrol function 1 g-04 or a V2V application server 1 g-05.

FIG. 1H is a view illustrating a block configuration of a terminalaccording to the disclosure.

As illustrated in FIG. 1H, the terminal according to an embodiment ofthe disclosure includes a transceiver 1 h-05, a controller 1 h-10, amultiplexer and demultiplexer 1 h-15, upper layer processor 1 h-20 and 1h-25, and control message processor 1 h-30.

The transceiver 1 h-05 receives data and a predetermined control signalthrough a forward channel of a serving cell, and transmits data and apredetermined control signal through a reverse channel. When a pluralityof serving cells are configured, the transceiver 1 h-05 performs datatransmission/reception and control signal transmission/reception throughthe plurality of serving cells. The multiplexer and demultiplexer 1 h-15multiplexes data generated by the upper layer processors 1 h-20 and 1h-25 or the control message processor 1 h-30 or transmits data receivedfrom the transceiver 1 h-05 to transmit the same to the appropriateupper layer processor 1 h-20 and 1 h-25 or the control message processor1 h-30. The control message processor 1 h-30 transmits and receives acontrol message from the base station and takes necessary actions. Theaction includes a function of processing control messages such as RRCmessages and MAC CE, reporting of CBR measurement values, and receptionof RRC messages for resource pool and terminal operation. The upperlayer processors 1 h-20 and 1 h-25 refer to DRB devices and may beconfigured for each service. The upper layer processors 1 h-20 and 1h-25 process data generated from user services such as file transferprotocol (FTP) or voice over Internet protocol (VoIP) and deliver themto the multiplexing and demultiplexing units (1 h-15), or process thedata transmitted from the multiplexer and demultiplexer 1 h-15 andtransmit the processed data to the upper layer service application. Thecontroller 1 h-10 identifies the scheduling command received through thetransceiver 1 h-05, for example, reverse grants, and controls thetransceiver 1 h-05 and the multiplexer and demultiplexer 1 h-15 so thatreverse transmission is performed with the appropriate transmissionresource at the appropriate time. Meanwhile, in the above, it has beendescribed that the terminal is composed of a plurality of blocks andeach block performs a different function, but this is only an exemplaryembodiment and is not limited thereto. For example, the controller 1h-10 itself may perform a function performed by the demultiplexer 1h-15.

FIG. 1I is a block diagram showing the configuration of a base stationaccording to the disclosure.

The base station apparatus of FIG. 1 i includes a transceiver 1 i-05, acontroller 1 i-10, a multiplexer and demultiplexer 1 i-20, a controlmessage processor 1 i-35, upper layer processors 1 i-25 and 1 i-30, anda scheduler 1 i-15.

The transceiver 1 i-05 transmits data and a predetermined control signalthrough a forward carrier and receives data and a predetermined controlsignal through a reverse carrier. When multiple carriers are configured,the transceiver 1 i-05 performs data transmission/reception and controlsignal transmission/reception through the multiple carriers. Themultiplexer and demultiplexer 1 i-20 multiplexes data generated by theupper layer processors 1 i-25 and 1 i-30 or the control messageprocessor 1 i-35 or demultiplexes the data received from the transceiver1 i-05 to transmit the same to the appropriate upper layer processors 1i-25 and 1 i-30, the control message processor 1 i-35, or the controller1 i-10. The control message processor 1 i-35 receives an instructionfrom the controller, generates a message to be transmitted to theterminal, and transmits the generated message to a lower layer. Theupper layer processors 1 i-25 and 1 i-30 may be configured for eachterminal-specific service, process data generated from user servicessuch as FTP or VoIP and transmit the data to the multiplexing anddemultiplexing unit 1 i-20, or process the data transmitted from themultiplexer and demultiplexer 1 i-20 and transmit the data to the upperlayer service application. The scheduler 1 i-15 allocates transmissionresources to the terminal at an appropriate time in consideration of thebuffer status of the terminal, channel status, and active time of theterminal, and processes the signal transmitted by the terminal to thetransceiver or transmits the signal to the terminal.

In the specific embodiments of the disclosure described above, theconstituent elements included in the disclosure are expressed in thesingular or plural according to the presented specific embodiment.However, the singular or plural expression is selected appropriately forthe situation presented for convenience of description, and thedisclosure is not limited to the singular or plural constituentelements, and even constituent elements expressed in plural are composedof the singular or singular. Even a component expressed in plural may becomposed of a singular number, or even a component expressed in asingular number may be composed of plural.

Meanwhile, although specific embodiments have been described in thedetailed description of the disclosure, various modifications may bemade without departing from the scope of the disclosure. Therefore, thescope of the disclosure should not be limited to the describedembodiments and should not be defined by the scope of the claims to bedescribed later, as well as the scope and equivalents of the claims.

In addition, the disclosure can be summarized as follows.

1. Definition of service-specific resource pool to support diverse R16V2X services both for the serving cell and for the inter-frequency.

2. Co-existence of service-specific resource pool and service-agnosticresource pool.

3. Classification of V2X services, based on PPPP, range, PPPR, Prose L2ID or a combination of the above information.

In addition, the disclosure can be summarized as follows.

1. UE←V2X server: Parameter provisioning

-   -   The mapping information of Destination Layer-2 ID(s) and the V2X        services, e.g. PSID, ITS-AIDs, ES, platooning . . . .    -   The mapping information of services to V2X frequencies/RATs (LTE        or NR or both)    -   The mapping information of services to range (high, medium, low)    -   The mapping information of services to PPPP    -   The mapping information of services to PPPR

2. UE interested in V2X service x: Camping on a V2X frequency of HPLMNmapped to service x

3. UE: Receiving V2X system information, the V2X system information mayinclude at least one of the following information.

-   -   Serving frequency        -   Service-specific resource pools        -   Service-agnostic resource pools    -   Inter-frequency        -   Service-specific resource pools        -   Service-agnostic resource pools    -   Inter-RAT        -   Service-specific resource pools        -   Service-agnostic resource pools    -   Service-specific resource pools        -   RAT information (optional; present only if it is included in            Inter-RAT branch)            -   E-UTRA or NR        -   Mapped services            -   List of mapped services        -   Range, PPPP, Destination L2 ID or combination of them        -   Resource Pool configuration            -   Time domain resource: bitmap            -   Frequency domain resource . . . .            -   SCS (If it is NR) and CP length)        -   Transmission power configuration            -   Maximum allowed transmission power        -   Resource sensing parameters    -   Service-agnostic resource pool        -   RAT information        -   Resource pool configuration        -   Transmission power configuration        -   Resource sensing parameters

4. Determining the frequencies/RATs for monitoring

-   -   1st set of the monitoring frequencies/RATs:        -   Intersection of frequencies mapped with the concerned V2X            service and the frequencies indicated supporting V2X in the            system information    -   2nd set of the monitoring frequencies/RATs:        -   Intra-RAT frequencies/inter-RAT frequencies providing            service specific pool for Service x    -   UE monitors the service specific pools of the 2nd set    -   If none of the frequencies provide the service specific pool for        service x    -   UE monitors service agnostic pools of 1st set

5. Determining the frequencies/RATs for transmission

-   -   UE transmits the data for service X in the service specific        resource pool of X in the serving frequency (if supported) or in        the non-serving frequency (if not supported by serving        frequency)

Second Embodiment

Hereinafter, the operating principle of the disclosure will be describedin detail with reference to the accompanying drawings. In the followingdescription of the disclosure, when it is determined that a detaileddescription of a related known function or configuration mayunnecessarily obscure the subject matter of the disclosure, the detaileddescription thereof will be omitted. In addition, terms to be describedlater are terms defined in consideration of functions in the disclosure,which may vary according to the intention or custom of users andoperators. Therefore, the definition should be made based on thecontents throughout this specification. Terms for identifying an accessnode used in the following description, terms for network entities,terms for messages, terms for interfaces between network objects, termsreferring to various identification information, and the like areexemplified for convenience of description. Therefore, the disclosure isnot limited to the terms described below, and other terms referring toobjects having an equivalent technical meaning may be used.

For convenience of description below, the disclosure uses terms andnames defined in the 3rd generation partnership project long termevolution (3GPP LTE) standard. However, the disclosure is not limited bythe terms and names, and can be applied equally to systems conforming toother standards.

FIG. 2A is a view illustrating a structure of an LTE system referred tofor description of the disclosure.

Referring to FIG. 2A, as illustrated, the radio access network of theLTE system is composed of next-generation base stations (evolved node B,hereinafter eNB, Node B or base station) 2 a-05, 2 a-10, 2 a-15, 2 a-20,an MME 2 a-25, and an S-GW 2 a-30. A user equipment (hereinafter, UE orterminal) 2 a-35 access an external network through the eNB 2 a-05˜2a-20 and the S-GW 2 a-30.

In FIG. 2A, the eNB 2 a-05˜2 a-20 correspond to the existing Node B ofthe UMTS system. The eNB is connected to the UEs 2 a-35 through a radiochannel and performs a more complex role than the existing Node B.Since, in the LTE system, all user traffic, including real-time servicessuch as VoIP through Internet protocol, are serviced through a sharedchannel, a device for scheduling by collecting state information such asbuffer status, available transmission power status, and channel statusof UEs is required, and the eNBs 2 a-05 to 2 a-20 are in charge. One eNBtypically controls multiple cells. For example, in order to implement atransmission rate of 100 Mbps, the LTE system uses, for example, anorthogonal frequency division multiplexing scheme (OFDM) in a 20 MHzbandwidth as a radio access technology. In addition, an adaptivemodulation coding (AMC) method is applied to determine a modulationscheme and a channel coding rate according to a channel state of theterminal.

The S-GW 2 a-30 is a device that provides a data bearer, and generatesor removes a data bearer under the control of the MME 2 a-25. The MME isa device responsible for various control functions as well as mobilitymanagement functions for a terminal, and is connected to a plurality ofbase stations.

FIG. 2B is a view illustrating a radio protocol structure in the LTEsystem of the disclosure.

Referring to FIG. 2B, the radio protocol structure in the LTE systemincludes PDCPs 2 b-05 and 2 b-40, RLCs 2 b-10 and 2 b-35, and MACs 2b-15 and 2 b-30 in a terminal and eNB, respectively. The PDCPs 2 b-05and 2 b-40 are in charge of operations such as IP headercompression/restore. The main functions of the PDCP are summarized asfollows.

-   -   Header compression and decompression: ROHC only    -   Transfer of user data    -   In-sequence delivery of upper layer PDUs at PDCP        re-establishment procedure for RLC AM    -   For split bearers in DC (only support for RLC AM): PDCP PDU        routing for transmission and PDCP PDU reordering for reception    -   Duplicate detection of lower layer SDUs at PDCP re-establishment        procedure for RLC AM    -   Retransmission of PDCP SDUs at handover and, for split bearers        in DC, of PDCP PDUs at PDCP data-recovery procedure, for RLC AM    -   Ciphering and deciphering    -   Timer-based SDU discard in uplink

The radio link controls (RLCs) 2 b-10 and 2 b-35 reconstruct the PDCPPDU to an appropriate size and performs an ARQ operation. The mainfunctions of RLCs are summarized as follows.

-   -   Transfer of upper layer PDUs    -   Error Correction through ARQ (only for AM data transfer)    -   Concatenation, segmentation and reassembly of RLC SDUs (only for        UM and AM data transfer)    -   Re-segmentation of RLC data PDUs (only for AM data transfer)    -   Reordering of RLC data PDUs (only for UM and AM data transfer    -   Duplicate detection (only for UM and AM data transfer)    -   Protocol error detection (only for AM data transfer)    -   RLC SDU discard (only for UM and AM data transfer)    -   RLC re-establishment

The MACs 2 b-15 and 2 b-30 are connected to several RLC layer entitiesconfigured in one UE, and perform an operation of multiplexing RLC PDUsto MAC PDUs and demultiplexing RLC PDUs from MAC PDUs. The mainfunctions of MAC are summarized as follows.

-   -   Mapping between logical channels and transport channels    -   Multiplexing/demultiplexing of MAC SDUs belonging to one or        different logical channels into/from transport blocks (TB)        delivered to/from the physical layer on transport channels    -   Scheduling information reporting    -   Error correction through HARQ    -   Priority handling between logical channels of one UE    -   Priority handling between UEs by means of dynamic scheduling    -   MBMS service identification    -   Transport format selection    -   Padding

The physical layers 2 b-20 and 2 b-25 channel-code and modulate upperlayer data, convert the same into OFDM symbols, and transmit the same tothe radio channel, or demodulate OFDM symbols received through the radiochannel, channel-decode the same, and transmit the same to the upperlayer. In addition, the physical layer also uses hybrid ARQ (HARQ) foradditional error correction, and the receiving end transmits thereception of the packet transmitted by the transmitting end in 1 bit.This is called HARQ ACK/NACK information. Downlink HARQ ACK/NACKinformation for uplink transmission may be transmitted through aphysical hybrid-ARQ indicator channel (PHICH), and uplink HARQ ACK/NACKinformation for downlink transmission may be transmitted through aphysical uplink control channel (PUCCH) or a physical uplink sharedchannel (PUSCH).

Meanwhile, the PHY layer may consist of one or a plurality offrequencies/carriers, and a technology for simultaneously configuringand using a plurality of frequencies is referred to as a carrieraggregation (hereinafter referred to as “CA”) technology. Through CAtechnology, only one carrier has been used for communication between theterminal and the base station (E-UTRAN NodeB, eNB), but the amount oftransmission can be dramatically increased by the number of subcarriersby additionally using a main carrier and one or a plurality ofsubcarriers. Meanwhile, in LTE, a cell in a base station using a primarycarrier is called a primary cell (PCell), and a subcarrier is called asecondary cell (SCell).

Although not shown in this figure, there is a radio resource control(hereinafter referred to as “RRC”) layer, respectively, above the PDCPlayer of the terminal and the base station, and the RRC layer maytransmit and receive access and measurement-related configurationcontrol messages for radio resource control.

FIG. 2C is a view illustrating the structure of a next-generation mobilecommunication system to which the disclosure is applied.

Referring to FIG. 2C, as illustrated, the radio access network of anext-generation mobile communication system is composed ofnext-generation base station (NR NB) 2 c-10 and NR CN (or nextgeneration core network (NG CN)) 2 c-05. The user terminal (NR UE orterminal) 2 c-15 accesses an external network through the NR NB 2 c-10and the NR CN 2 c-05.

In FIG. 2 c , the NR NB 2 c-10 corresponds to the eNB of the existingLTE system. The NR NB is connected to the NR UE 2 c-15 through a radiochannel and can provide a service superior to that of the existing NodeB. In the next-generation mobile communication system, since all usertraffic is serviced through a shared channel, a device that collects andschedules status information such as buffer status, availabletransmission power status, and channel status of UEs is required, andthe NR NB 2 c-10 is in charge.

One NR NB typically controls multiple cells. In order to implementultra-high-speed data transmission compared to the existing LTE, it mayhave more than the existing maximum bandwidth, and additionalbeamforming technology may be grafted using orthogonal frequencydivision multiplexing (OFDM) as a wireless access technology. Inaddition, an adaptive modulation coding (AMC) method is applied todetermine a modulation scheme and a channel coding rate according to achannel state of the terminal.

The NR CN 2 c-05 performs functions such as mobility support, bearerconfiguration, and QoS configuration. The NR CN is a device responsiblefor various control functions as well as a mobility management functionfor a terminal, and is connected to a plurality of base stations. Inaddition, the next-generation mobile communication system can beinterlocked with the existing LTE system, and the NR CN is connected tothe MME 2 c-25 through a network interface. The MME is connected to theexisting eNB 2 c-30.

FIG. 2D is a view illustrating a radio protocol structure of anext-generation mobile communication system to which the disclosure isapplied.

Referring to FIG. 2D, the radio protocol structure of a next-generationmobile communication system is composed of NR PDCPs 2 d-05 and 2 d-40,NR RLCs 2 d-10 and 2 d-35, and NR MACs 2 d-15 and 2 d-30 in a terminaland NR base station, respectively. The main functions of the NR PDCPs 2d-05 and 2 d-40 may include some of the following functions.

-   -   Header compression and decompression: ROHC only    -   Transfer of user data    -   In-sequence delivery of upper layer PDUs    -   PDCP PDU reordering for reception    -   Duplicate detection of lower layer SDUs    -   Retransmission of PDCP SDUs    -   Ciphering and deciphering    -   Timer-based SDU discard in uplink

In the above, the reordering function of the NR PDCP device refers to afunction of reordering PDCP PDUs received from a lower layer in orderbased on a PDCP sequence number (SN), may include the function ofpassing data to the upper layer in the order of reordering, may includea function of reordering the order to record the lost PDCP PDUs, mayinclude a function of reporting the status of the lost PDCP PDUs to thesender, and may include a function of requesting retransmission of lostPDCP PDUs.

The main functions of the NR RLCs 2 d-10 and 2 d-35 may include some ofthe following functions.

-   -   Transfer of upper layer PDUs    -   In-sequence delivery of upper layer PDUs    -   Out-of-sequence delivery of upper layer PDUs    -   Error Correction through ARQ    -   Concatenation, segmentation and reassembly of RLC SDUs    -   Re-segmentation of RLC data PDUs    -   Reordering of RLC data PDUs    -   Duplicate detection    -   protocol error detection    -   RLC SDU discard    -   RLC re-establishment

In the above, the in-sequence delivery function of the NR RLC devicerefers to a function of sequentially delivering RLC SDUs received from alower layer to an upper layer, may include a function of reassemblingand delivering when one RLC SDU is originally divided into multiple RLCSDUs and received, may include a function of rearranging received RLCPDUs, based on an RLC sequence number (SN) or a PDCP sequence number(SN), may include a function of rearranging the order and recording thelost RLC PDUs, may include a function of reporting the status of lostRLC PDUs to the transmitting side, may include a function of requestingretransmission of lost RLC PDUs, may include a function of transferringonly RLC SDUs up to before the lost RLC SDU to an upper layer in orderwhen there is a lost RLC SDU, may include a function of sequentiallydelivering all RLC SDUs received before the timer starts to an upperlayer even if there is a lost RLC SDU, if a predetermined timer hasexpired, and may include a function of sequentially delivering all RLCSDUs received so far to the upper layer even if there is a lost RLC SDU,if a predetermined timer has expired. In addition, RLC PDUs may beprocessed in the order of reception (regardless of the order of serialnumber and sequence number, in the order of arrival) and delivered tothe PDCP device regardless of the order (out-of-sequence delivery), andin the case of a segment, segments stored in a buffer or to be receivedin the future may be received, reconstructed into a complete RLC PDU,processed, and delivered to the PDCP device. The NR RLC layer may notinclude a concatenation function, and the function may be performed inthe NR MAC layer or may be replaced by a multiplexing function of the NRMAC layer.

In the above, the out-of-sequence delivery function of the NR RLC devicerefers to a function of directly delivering RLC SDUs received from alower layer to an upper layer regardless of order, may include afunction of reassembling and delivering when one RLC SDU is originallydivided into multiple RLC SDUs and received, and may include a functionof storing the RLC SNs or PDCP SNs of received RLC PDUs, sorting theorder, and recording the lost RLC PDUs.

The NR MACs 2 d-15 and 2 d-30 may be connected to several NR RLC layerentities configured in one terminal, and the main functions of the NRMAC may include some of the following functions.

-   -   Mapping between logical channels and transport channels    -   Multiplexing/demultiplexing of MAC SDUs    -   Scheduling information reporting    -   Error correction through HARQ    -   Priority handling between logical channels of one UE    -   Priority handling between UEs by means of dynamic scheduling    -   MBMS service identification    -   Transport format selection    -   Padding

The NR PHY layers 2 d-20 and 2 d-25 may channel-code and modulate theupper layer data, make the same into OFDM symbols, and transmits thesame over a wireless channel, or may demodulate the OFDM symbol receivedthrough a radio channel, decode the channel, and transmit the same to anupper layer.

Although not illustrated in this figure, there is a radio resourcecontrol (hereinafter referred to as “RRC”) layer, respectively, abovethe PDCP layer of the terminal and the base station, and the RRC layertransmits and receives access and measurement-related configurationcontrol messages for radio resource control.

FIG. 2E is a view illustrating V2X communication within the cellularsystem of the disclosure.

V2X collectively refers to communication technology through allinterfaces with the vehicle, and may include V2V, V2I, V2P, V2N, and thelike according to the form and communication elements. The V2P and V2Vbasically follow the structure and operation principle of Rel-13inter-device communication (D2D). That is, it is based on a sidelink(PC5) operation, and actual data packets may be transmitted and receivedthrough a sidelink, which is a transmission channel between theterminals, not the uplink and downlink of the base station and theterminal. This basic concept can be applied not only to V2X defined inLTE, but also to V2X that can be newly defined in NR, and upgrades forspecific scenarios can be applied.

The base station 2 e-01 may communicate with at least one of vehicleterminals 2 e-05 and 2 e-10 and a pedestrian portable terminal 2 e-15located in the cell 2 e-02 supporting V2X. For example, the vehicleterminal 2 e-05 can perform cellular communication with the base station2 e-01 using the vehicle terminal-base station link (Uu, 2 e-30, 2e-35), and may perform device-to-device communication with anothervehicle terminal 2 e-10 or a pedestrian's portable terminal 2 e-15 usingside link PC5s 2 e-20 and 2 e-25.

In the above, the base station may be an upgraded eNB supporting gNB orNR. In order for the vehicle terminals 2 e-05 and 2 e-10 and thepedestrian mobile terminal 2 e-15 to directly transmit and receiveinformation using the sidelink (2 e-20, 2 e-25), the base station shouldallocate a resource pool that can be used for sidelink communication. Amethod of allocating resources by a base station to a terminal in V2X ofthe LTE system is described below, and a similar approach as in the LTEmay be applied in V2X introduced in the NR system. However, in NR,different numerology is used, and the design of the sidelink resourcepool may be somewhat different.

Based on the V2X of the LTE system, it can be divided into two types:scheduled resource allocation (mode 3) and UE autonomous resourceallocation (mode 4) according to how the base station allocatesresources to the terminal.

The scheduled resource allocation is a method in which the base stationallocates resources used for sidelink transmission to RRC-connectedterminals in a dedicated scheduling scheme. The method is effective forinterference management and resource pool management (dynamicallocation, semi-persistence transmission) because the base station canmanage the resources of the sidelink. In addition, in the case ofscheduled resource allocation (mode 3) in which the base stationallocates and manages resources for V2X, when the RRC connected terminalhas data to be transmitted to other terminals, the terminal may transmita resource allocation request to the base station using an RRC messageor a MAC control element (CE). Here, the RRC message may be aSidelinkUEInformation or UEAssistanceInformation message. Meanwhile, asan example of the MAC CE may, a buffer status report MAC CE of a newformat (including at least an indicator indicating that a buffer statusreport for V2X communication and information on the size of databuffered for sidelink communication) may be used. For detailed formatand contents of the buffer status report used in 3GPP, refer to 3GPPstandard TS36.321 “E-UTRA MAC Protocol Specification”.

On the other hand, UE autonomous resource allocation is a method inwhich the base station provides a sidelink transmission/receptionresource pool for V2X to a terminal as system information, and theterminal selects a resource pool according to a predetermined rule. Theresource selection method may include zone mapping, sensing-basedresource selection, and random selection.

The structure of the resource pool for V2X may be configured in a mannerin which resources 2 e-40, 2 e-50, 2 e-60 for scheduling allocation (SA)and resources 2 e-45, 2 e-55, 2 e-65 for data transmission are adjacentto each other to form one subchannel, or may be configured in a mannerin which the resources 2 e-70, 2 e-75, 2 e-80 for SA and the resources 2e-85, 2 e-90, 2 e-95 for data transmission are not adjacent. Regardlessof which of the above two structures is used, the resource for the SAconsists of two consecutive PRBs and includes information indicating thelocation of the resource for transmitting data. The number of terminalsreceiving the V2X service in one cell may be multiple, and therelationship between the base station 2 e-01 and the terminals 2 e-05, 2e-10, 2 e-15 described above may be extended and applied.

In addition, in order to transmit and receive sidelink data through theresource pool, V2X service is basically classified through a destinationlayer2 ID (or destination ID) in the V2X of the LTE system. That is, thesource/destination layer2 ID (each 24 bit size) of the terminal isincluded in the header of the V2X data packet transmitted through thesidelink, that is, the MAC PDU, the source layer2 ID means the uniqueidentifier of the terminal, and the destination layer2 ID indicates theservice type of V2X data traffic delivered by the terminal.

If the other terminal, which has received the destination layer2 IDtransmitted by the transmission terminal, subscribes to and isconfigured to receive the service for the corresponding destinationlayer2 ID, the data packet belonging to the corresponding MAC PDU isdecoded and delivered to the upper layer. The mapping information forthe destination layer2 ID and the V2X data packet is transferred fromthe V2X server to the V2X control function and provisioned to theterminal.

FIG. 2F is a view illustrating a data transmission procedure of a V2Xterminal operating in mode 3 in an LTE system of the disclosure.

Referring to FIG. 2F, terminal 1 2 f-01 camping on (2 f-05) may receivesystem information (SIB21) for V2X from the base station 2 f-03 (2f-10).

The system information may include at least one of resource poolinformation for sidelink data transmission/reception, configurationinformation for a sensing operation, information for configuringsynchronization, and information for inter-frequencytransmission/reception. When data traffic for V2X is generated interminal 1 2 f-01 (2 f-15), RRC connection with the base station may beperformed (2 f-20). The above RRC connection process may be performedbefore data traffic is generated (2 f-15).

The terminal 1 2 f-01 requests a transmission resource capable of V2Xcommunication with other terminals 2 f-02 from the base station (2f-25). At this time, the base station may be requested by using an RRCmessage or MAC CE. Here, the RRC message may be a SidelinkUEInformationor UEAssistanceInformation message. Meanwhile, as an example, the MAC CEmay be a buffer status report MAC CE of a new format (including at leastan indicator indicating that a buffer status report for V2Xcommunication and information on the size of data buffered for sidelinkcommunication).

The base station 2 f-03 allocates a V2X transmission resource to theterminal 1 (2 f-01) (2 f-30). The base station 2 f-03 may allocate V2Xtransmission resources through a dedicated RRC message, and the messagemay be included in the RRCConnectionReconfiguration message.

The resource allocation may be a V2X resource scheduled from the basestation through the Uu interface according to the type of trafficrequested by the terminal or whether the corresponding link iscongested, or a resource directly selected by the terminal from aresource pool (resource for PC5) provided by the base station. In orderto determine the resource allocation, the terminal may add and transmitPPPP or logical channel identifier (LCID) information of the V2X trafficthrough UEAssistanceInformation or MAC CE. Since the base station alsoknows information on the resources used by other terminals, the basestation schedules a resource requested by the terminal 1 2 f-01 amongremaining resources.

In addition, when the RRC message includes SPS configuration informationthrough Uu, the base station may activate the SPS by transmitting DCIthrough the PDCCH (2 f-35). Terminal 1 2 f-01 may select a transmissionlink and a resource according to the resource and transmission methodallocated from the base station 2 f-03 (2 f-40), and transmit data tothe terminals 2 f-02 (2 f-45).

FIG. 2G is a view illustrating a data transmission procedure of a V2Xterminal operating in mode 4 according to the disclosure.

Unlike mode 3, in which a base station (2 g-03) is directly involved inresource allocation, there is a difference in that, in mode 4 operation,terminal 1 2 g-01 autonomously selects resources and transmits databased on the resource pool previously received through systeminformation.

In V2X communication, the base station 2 g-03 may allocate several typesof sidelink resource pools (V2V resource pool, V2P resource pool) forterminal 1 2 g-01. The resource pool may consist of a resource pool inwhich the terminal can autonomously select an available resource poolafter sensing resources used by other terminals around it, and aresource pool in which the terminal randomly selects a resource from apreconfigured resource pool.

Referring to FIG. 2G, terminal 1 2 g-01 camping on (2 g-05) may receivesystem information SIB21 for V2X (2 g-10) from a base station 2 g-03.

The system information may include at least one of resource poolinformation for signal transmission/reception, configuration informationfor sensing operation, information for configuring synchronization, andinformation for inter-frequency transmission/reception.

When data traffic for V2X is generated (2 g-15) in terminal 1 2 g-01,the terminal 1 2 g-01 may select a resource in the time/frequency domain(2 g-20) and transmit data to other terminals 2 g-02 according to theconfiguration information (transmission operation configured for theresource pool (dynamic allocation one-time transmission, dynamicallocation multiple transmission, sensing-based one-time transmission,sensing-based multiple transmission, random transmission)) receivedthrough the system information from the base station 2 g-03 (2 g-25).

In general, since the V2X service in LTE is implemented for the purposeof periodic transmission of the location information of safety-relatedterminals, the terminal can perform sensing-based multiple transmissionin mode 4 operation. That is, the terminal may sense resources throughwhich signals are transmitted by other terminals, select a transmittableresource block in the resource pool in which the correspondingtransmission is performed, and reserve resources so that they can betransmitted periodically thereafter. Thereafter, if the data packetgenerated by the terminal is changed or disappears, the terminalrestarts or cancels the above sensing and resource reservation operationso that a new data packet can be delivered. As described above, sensingand resource reservation-based multi-transmission may be basicallyoperated, and if the sensing operation is not well performed,communication may be performed through random resource selection from acorresponding resource pool.

FIG. 2F and FIG. 2G above summarize the configuration and overalloperation of sidelink data transmission and reception in the V2X system,and the packet design, radio bearer configuration, and encryption methodin the user plane for the actually transmitted data packets are brieflydescribed in FIG. 2E or some of them are omitted. In order to newlydefine the NR V2X system, it may be necessary to redefine not only theoverall resource pool configuration, but also the packet design in theuser plane, radio bearer configuration, and encryption method. In thedisclosure, a user plane operation and a radio bearer management overalloperation for NR V2X are proposed in a later embodiment.

FIG. 2H is a view illustrating a MAC PDU format applied to an NR V2Xsystem proposed in the disclosure.

In addition to the LTE V2X system, the NR V2X system basicallypresupposes data transmission and reception between the terminal and theterminal as a basic scenario. To this end, a definition of a sidelinkdifferent from the existing cellular-based uplink and downlink and adata transmission/reception format through the corresponding sidelinkshould be determined. When a V2X data packet is actually generated inthe terminal, the MAC is configured to transmit MAC PDU through internalPDCP and RLC operation. In general, the RLC and PDCP operations willfollow the operation defined in LTE or NR as it is, and it is necessaryto apply the actually transmitted MAC PDU configuration according to thesidelink.

The disclosure proposes a transmission format of an NR V2X system,particularly a MAC PDU delivered through a sidelink, and MAC PDUs arelargely classified into a MAC PDU header, a MAC PDU sub-header, and aMAC SDU.

First, as can be seen in 2 h-05 to 2 h-50, the disclosure proposes astructure of a MAC PDU header+m×(MAC PDU sub-header+MAC SDU) as anoverall structure of a MAC PDU. Here, m denotes the total number of MACSDUs and related sub-header transmitted through the MAC PDU, and unlikein the LTE V2X system, a related MAC sub-header is located in front ofthe MAC SDU for each MAC SDU. For reference, in the LTE V2X system, theMAC PDU has a structure of MAC PDU header+m×MAC PDU sub-header+m×MACSDU. In addition, as an option, a padding byte for matching the MAC PDUsize may be included.

Through the above MAC PDU structure, the MAC PDU received by theterminal can be sequentially processed at the same time as it isdecoded, thereby having an advantage in data processing having a highspeed and a high data rate. Currently, LTE V2X data traffic onlysupports safety-related services including 300 bytes of locationinformation, whereas NR supports various services, especially advanceddriving, extended sensor, platooning service, and so on, so that NR V2Xrequires a higher data rate than LTE V2X. Therefore, the MAC PDUstructure proposed above may be helpful for high-speed data processing.

Specifically, looking at the structure of the MAC PDU header in NR V2Xproposed by the disclosure in detail, the MAC PDU header has a structureof V/R/SRC/DST.

Here, the V field 2 h-55 is a field indicating the version of thecorresponding MAC PDU, and may consist of 4 bits. The V field is a fieldthat distinguishes between Rel-12/13 D2D and Rel-14/15 V2X and newlydefined NR V2X. The V field may have a different value from the previousRel-12/13 D2D and Rel-14/15 V2X, and the terminal receiving the same maydecode the corresponding field to identify the purpose and method forwhich the MAC PDU has been delivered.

The R field 2 h-60 of the MAC PDU header is a bit reserved foradditional functions that can be used later.

The SRC field 2 h-65 of the MAC PDU header means a terminal source layer2 ID of 24 bits, and is mapped to a unique ID specified for eachterminal. The corresponding SRC field may be updated and applied whenthe terminal receives a V2X related parameter from the V2X server, andmay be recorded and applied in the own USIM of the terminal.

The DST field 2 h-70 of the MAC PDU header means a destination layer 2ID of 24 bits, and may be mapped to distinguish which service is foreach V2X service. In other words, having the same DST value means thatthe same V2X service is being delivered. However, since NR V2X is notintended for broadcast only, a 24-bit DST may be configured as a uniqueID of the terminal to support unicast, or the terminal may be specifiedthrough some bits of the 24-bit DST. For example, in 24 bits DST, MSB 16bits may indicate a service type, and LSB 8 bits may indicate a terminalID. The DST may be provided through a V2X server and a V2X controlfunction, or may be recorded in a USIM inside the terminal.

Additionally, the structure of the sub-header of the NR V2X MAC PDU mayhave a structure of R/F/LCID/L.

The MAC PDU sub-header may be used for the purpose of indicating thesize of the MAC SDU to be transmitted. The R fields 2 h-75 and 2 h-95 ofthe MAC PDU sub-header are bits reserved for additional functions thatcan be used later.

The F fields 2 h-80 and 2 h-100 of the MAC PDU header may serve toindicate the size of the subsequent L fields 2 h-90 and 2 h-110, if theF field is configured as 0, it may mean that the L field is 8 bits (2h-90), and when the F field is configured as 1, the L field may mean 16bits (2 h-110). Alternatively, it can be configured in reverse.

In addition, the LCID fields 2 h-85 and 2 h-105 of the MAC PDUsub-header are values for classifying the logical channel type of thetransmitted MAC SDU, and may be mapped into a table according to the SLdata type and organized. The LCID is determined within the terminal, andthe terminal may designate to map V2X traffic generated by a certainLCID.

FIG. 2I is a view illustrating sidelink radio bearer management,encryption and decryption methods applied to the NR V2X system proposedin the disclosure.

If the sidelink radio bearer in NR V2X is defined as a sidelink resourcebearer (SLRB), the SLRB may be composed of a PDCP entity and an RLCentity. That is, SLRB=PDCP entity+RLC entity. In this case, one SLRB maybe divided into a pair of LCID and SRC/DST. That is, the terminal mayestablish a new SLRB when receiving an unknown LCID or SRC/DST pair bydecoding the contents included in the header and subheader of the MACPDU packet received from another terminal. The operation of establishinga new SLRB refers to an operation of initializing PDCL/RLC entitiesconstituting the SLRB, and the values of the state/timer variables maybe initialized. Specifically, initialization may be performed accordingto the following procedure.

1. Configuring the T_reassembly (RLC) and T_reordering (PDCP) values to0 (this means reconfiguring the timer for reassembly and reordering inRLC and PDCP.)

2. Configuring RLC state variables (Since it is possible to receive datafrom other terminals in V2X, it is necessary not to configure the RLC SNreceived from the terminal to 0, but based on the RLC SN value of thefirst received packet.)

A. RX_Next_Reassembly is configured based on the SN of the firstreceived segment

B. RX_Next_Highest is configured based on the SN of the first receivedsegment

In this case, the terminal may configure based on the RLC SN valuereceived as described above in case of performing V2X communication bybroadcast, whereas, in case of performing V2X communication throughunicast, a method of configuration as 0 may be used.

3. Configuring PDCP state variables

A. RX_NEXT is configured based on the SN of the PDCP PDU that firstreceived

B. RX_DELIV is configured based on the SN of the first PDCP PDU received

The RX_NEXT indicates the PDCP SN expected to be received next. Theinitial value can be configured as 0.

RX_DELIV indicates a PDCP SDU that has not been delivered to an upperlayer but is waiting for transmission, and an initial value may beconfigured as 0.

In LTE, since there is no reordering function in the PDCP layer,received packets can be processed regardless of the SN. In this case,the reordering function means that packets received from the PDCP areprocessed in order and delivered to an upper level. On the other hand,the disclosure proposes a method of configuring PDCP state variables asdescribed above in consideration of reordering in PDCP.

At this time, like the above RLC state variable, the terminal can beconfigured based on the received PDCP SN value when performing V2Xcommunication by broadcast, whereas in the case of V2X communicationthrough unicast, a method of configuring as 0 can be used.

In addition, in the V2X service, since the service varies according tothe destination L2 ID (DST ID), an encryption technique is required thatprevents a terminal without authority for the corresponding service fromdecoding the corresponding data. For example, the SLRB is transmittedfor each specific service, and the corresponding SLRB has a root key forencryption for each DST ID. In this case, the actual key for encryptionis generated as a root key characterized by the DST ID, and additionalinformation necessary for the actual key may be included in the PDCPheader. To this end, different passwords may be applied for eachterminal and message (service). More detailed operation follows thefollowing procedure.

The NR V2X terminal 2 i-01 may perform a procedure for receiving serviceauthority through the V2X control function 2 i-02 to support the NR V2Xservice (2 i-05).

In the above procedure, the V2X control function (2 i-02) performsparameter provisioning for NR V2X service, and may transmit DST IDmapping for each service, V2X service supported for each RAT, V2Xsupportable frequency information, and the like. The above V2X controlfunction (2 i-02) receives and has the corresponding information throughthe V2X server (2 i-03) in advance, and when the corresponding terminalattempts to connect, it transmits the corresponding information to theterminal.

Thereafter, the terminal performs a key request to the V2X server foreach group (here, the group may be indicated for each DST ID) (2 i-10),and the V2X server provides a service key for each DST ID/group (2i-15). In the above, the V2X server providing the key may be a V2X keymanagement function, which may exist inside or outside the V2X server.In the disclosure, for convenience, it is described as a V2X server.

In addition, in step 2 i-20, the V2X server performs the procedure ofproviding the root key. That is, the root key extracted from the DST IDis assigned to the terminal, and the terminal may generate (or derive)an encryption key used for actual encryption by applying the DST ID tothe root key. In the above step, the V2X server may also provide expirytime to which the key is applied to the terminal.

When V2X data is generated, the terminal performs an exclusive logicaloperation (2 i-35) on the key stream block obtained through the keygeneration algorithm (2 i-30) for encryption of the terminal and thepure V2X data block to generate a ciphered user packet.

Here, the key stream block for encryption can be obtained afterperforming a key generation algorithm in which a key for encryption ofthe user plane obtained from the root key (Key_V2X) (2 i-25) andencryption parameters such as COUNT (for example, part of PDCP SN+KeyID), Bearer (Bearer ID), Direction (message delivery direction, 0 or 1),and Length (length of the key stream block) are input as inputs.

The reception terminal receives the encrypted user data packet, performsthe same key generation algorithm applied by the terminal, generates thesame key stream block as used for encryption, and performs exclusivelogical operation (2 i-45). Similar to algorithm execution in terminal,in the reception terminal (or applicable to the base station), a keystream block for encryption can be obtained by inputting a key forencryption of the user plane obtained from the Root Key (Key_V2X) (2i-25) and encryption parameters (COUNT, Bearer, Direction, Length(length of the key stream block)) as input parameters.

FIG. 2J is a view illustrating an overall operation of transmitting andreceiving data in a user plane in the NR V2X system proposed by thedisclosure.

Referring to FIG. 2J, in step 2 j-10, terminal 1 2 j-01 supporting NRV2X receives parameters for NR V2X service from V2X server 2 j-05(provisioning). At this time, the V2X server 2 j-05 may transferparameters related to NR V2X for the terminals to the V2X controlfunction 2 j-04 in advance, authenticate the terminal and transmit theparameters when the corresponding terminal requests the NR V2X serviceright in the V2X control function 2 j-04. The parameters transmitted inthe above step may include at least one of the following information.

-   -   Frequency information supporting LTE V2X and NR V2X    -   Mapping information between destination layer-2 ID(s) and V2X        service (for example, extended sensor, advanced driving,        platooning, etc. are mapped to PSID, ITS-AIDs, etc.)    -   Mapping between V2X service and V2X supported frequency/RAT (LTE        or NR), that is, a service supported by a specific frequency may        be specified

In step 2 j-15, the terminal 1 2 j-01 camps on a V2X frequencysupporting service x of interest. The V2X frequency may be a frequencysupported by HPLMN (Home PLMN). The frequency may be included in theparameter received in step 2 j-10.

In step 2 j-20, the terminal 1 2 j-01 receives the system informationfor the V2X service from the base station 2 j-03 camped on the V2Xfrequency. The system information may include information capable ofperforming a V2X operation, and representatively may include resourcepool information. In addition, the resource pool information includes atransmission resource pool and a reception resource pool, and theterminal 1 2 j-01, which received the information in step 2 j-25, mayimmediately receive V2X data from another V2X terminal 2 2 j-02 throughthe reception resource pool.

In step 2 j-30, the terminal, which received the V2X MAC PDU from thereception resource pool, decodes the header and sub-header existing inthe corresponding MAC PDU, distinguishes which service the received MACPDU is data for, and performs a first security handling operation(reception packet security application) for the SLRB to which theservice is delivered.

The first security handling operation is an operation of decoding databy decoding the received MAC PDU and performing appropriate decoding ona specific SLRB, which will be described in detail in FIGS. 2KA and 2KB.

When data is received through the sidelink and NR V2X data traffic to betransmitted from the terminal 1 occurs at the same time (2 j-35), theterminal prepares to transmit data through the transmission resourcepool received in step 2 j-20. Before actual data is transmitted, theterminal performs a second security handling operation (transmissionpacket security application). The second security handling operation isan operation of applying encryption to each SLRB to transmit a datapacket to be transmitted, and will be described in detail in FIGS. 2KAand 2KB.

When encryption of the data to be transmitted is completed, a MAC SDUand a header are configured and transmitted according to the MAC PDUformat proposed in FIG. 2H (2 j-45).

FIGS. 2KA and 2KB are views illustrating in detail a user plane radiobearer management and encryption operation of an NR V2X supportingterminal proposed in an embodiment of the disclosure.

In steps 2 k-05, the terminal supporting NR V2X receives (or receivesprovisioning) parameters for the NR V2X service from the V2X server. Atthis time, the V2X server may transmit NR V2X-related parameters forterminals to the V2X control function in advance, and when the terminalrequests NR V2X service authorization in the V2X Control Function, theterminal may be authenticated and parameters may be delivered. Theparameters transmitted in the above step have been described in detailin FIG. 2 j.

The terminal camps on a V2X frequency that supports the V2X service x ofinterest. The V2X frequency may be a frequency supported by HPLMN. Aterminal camping on the V2X frequency receives system information for aV2X service from a corresponding base station in step 2 k-10.

The system information may include information capable of performing aV2X operation, and representatively may include resource poolinformation. Also, the resource pool information may include atransmission resource pool and a reception resource pool.

Accordingly, the terminal receiving the corresponding information maymonitors the reception resource pool in step 2 j-15, and immediatelyreceive V2X data from another V2X terminal through the receptionresource pool.

When the terminal receives the NR V2X sidelink data packet, in step 2k-20, the terminal processes the received MAC PDU and performs a firstsecurity handling operation for transferring the received MAC PDU to anupper layer. In other words, the terminal may determine the service typeof the received packet by identifying the header and sub-header of thereceived MAC PDU. The terminal may distinguish whether the correspondingpacket is a new service or an existing service and operate accordingly.

In step 2 k-25, the terminal identifies whether there is a new LCID or anew SRC/DST pair in the subheader of the received MAC PDU.

If both conditions are not satisfied, the terminal decodes thecorresponding received packet in step 2 k-30. That is, the terminal mapsthe received packet to an existing SLRB separated from the LCID andSRC/DST, and decodes the data by applying a decryption key applied tothe SLRB. In particular, when data decoding is performed in the abovestep, the root key obtained from the DST ID and additional informationfor decoding included in the PDCP packet header are used.

If the terminal satisfies any of the two conditions in step 2 k-25, theterminal determines that the packet is indicated as a new service instep 2 k-35 and establishes a new SLRB. In other words, the terminalcreates an RLC and PDCP constituting a new SLRB, and initializes (orupdates) the RLC/PDCP state variable.

For example, if the received sub PDU is a UMD PDU, the terminaltransfers the sub PDU to the RLC entity, and if the sub PDU includes aUMD PDU segment, the RLC state variable is updated. At this time, theRLC state variable (RX_Next_Reassembly, RX_Next_Highest) is configuredas the RLC SN included in the received first UMD PDU segment. This isbecause the MAC PDU received by the terminal from another terminal maynot be an initial transmission but may be a transmission having anarbitrary RLC SN.

In step 2 k-40, it is determined whether the DST of the MAC PDU receivedby the terminal is first received, and if it corresponds to the firstDST ID, that is, a new service, the terminal corresponds to the DST IDreceived in steps 2 k-45. The encryption key is generated through theroot key. The key is used for decryption, and the SRC ID can also beapplied to the key generation algorithm. In the above step, additionallynecessary information, for example, key id information, when obtaining akey used for actual decoding may be included in the header of thereceiving PDCP.

When receiving the already applied DST ID again, the terminal decodesthe data packet by applying the known decoding key in steps 2 k-55.

At the same time as performing the above operation, NR V2X data trafficis generated independently from the terminal, and data can betransmitted through the transmission pool (2 k-65).

When the V2X data transmission is triggered, the terminal performs asecond security handling operation in steps 2 k-70. In other words, theterminal performs a process of generating a MAC PDU for transmitting adata packet to be transmitted.

In steps 2 k-75, the terminal may determine whether a data packet to betransmitted can be delivered to a service that is already in use, forexample, an established SLRB. That is, the terminal may determinewhether there is an SLRB (PDCP/RLC) corresponding to the data packet tobe transmitted.

If the service has already been used (i.e., there is a pre-establishedSLRB), the terminal can generate a PDCP PDU for delivery to the SLRB insteps 2 k-80. At this time, the terminal includes key id information,etc., used for PDCP PDU generation, in the PDCP header. Thereafter, theencryption key applied to the SLRB is applied, the PDCP PDU istransmitted to the RLC after encryption, and the MAC PDU is generatedand transmitted after adding the RLC header.

If the data traffic to be transmitted by the terminal is for a newservice, for example, a packet to be transmitted through a new SLRB, theterminal generates a PDCP/RLC entity in steps 2 k-85.

In addition, the terminal may identify whether it is the first packet tobe transmitted in steps 2 k-90. If it is the first packet, the terminalgenerates a root key for the packet to be transmitted using the DST IDin steps 2 k-95. In addition, the terminal generates an actualencryption key by applying the Root key and SRC ID to a key generationalgorithm.

Then, the terminal generates a PDCP PDU delivered to the SLRB in step 2k-100. At this time, the terminal includes the key id information usedin the PDCP header. In the above, the terminal transmits the encryptedPDCP PDU to the RLC by applying the generated encryption key, adds theRLC header, and generates and transmits the MAC PDU.

If the packet to be transmitted in steps 2 k-90 is not the first, theterminal generates a PDCP packet by applying the encryption key of theSLRB already applied, and generates and transmits a MAC PDU.

FIG. 2L is a view illustrating a block configuration of a terminalaccording to an embodiment of the disclosure.

As shown in FIG. 2L, the terminal according to an embodiment of thedisclosure includes a transceiver 2 l-05, a controller 2 l-10, amultiplexing and demultiplexing unit 2 l-15, and kinds of upper layerprocessors 2 l-20 and 2 l-25, and a control message processor 2 l-30.

The transceiver 2 l-05 receives data and a predetermined control signalthrough a forward channel of a serving cell and transmits data and apredetermined control signal through a reverse channel. When a pluralityof serving cells are configured, the transceiver 2 l-05 performs datatransmission/reception and control signal transmission/reception throughthe plurality of serving cells. The multiplexing and demultiplexing unit2 l-15 multiplexes data generated from the upper layer processing units2 l-20 and 2 l-25 or the control message processing unit 2 l-30, ordemultiplexes the data received from the transmission/reception unit 2l-05 and transfers it to the appropriate upper layer processing units (2l-20, 2 l-25) or control message processing units (2 l-30). The controlmessage processor 2 l-30 transmits and receives a control message fromthe base station and takes necessary actions. The action includes afunction of processing control messages such as RRC messages and MAC CE,reporting of CBR measurement values, and reception of RRC messages forresource pool and terminal operation. The upper layer processors 2 l-20and 2 l-25 refer to DRB devices and may be configured for each service.The upper layer processors 2 l-20 and 2 l-25 process data generated fromuser services such as file transfer protocol (FTP) or voice overInternet protocol (VoIP) and transfer the processed data to themultiplexing and demultiplexing unit (2 l-15), or process the datatransmitted from the multiplexing and demultiplexing unit 2 l-15 anddeliver the processed data to the service application of the upperlayer. The controller 2 l-10 checks the scheduling commands receivedthrough the transceiver 2 l-05, for example, reverse grants to controlthe transceiver 2 l-05 and the multiplexing and demultiplexing unit 2l-15 so that reverse transmission is performed with an appropriatetransmission resource at an appropriate time. Meanwhile, in the above,it has been described that the terminal is composed of a plurality ofblocks and each block performs a different function, but this is only anexemplary embodiment and is not limited thereto. For example, thecontroller 2 l-10 itself may perform a function that the demultiplexer 2l-15 performs.

FIG. 2M is a view illustrating a block configuration of a base stationaccording to an embodiment of the disclosure.

The base station of FIG. 2M includes a transceiver 2 m-05, a controller2 m-10, a multiplexing and demultiplexing unit 2 m-20, a control messageprocessor 2 m-35, kinds of upper layer processors 2 m-25 and 2 m-30, anda scheduler 2 m-15.

The transceiver 2 m-05 transmits data and a predetermined control signalthrough a forward carrier and receives data and a predetermined controlsignal through a reverse carrier. When multiple carriers are configured,the transceiver 2 m-05 performs data transmission/reception and controlsignal transmission/reception through the multiple carriers. Themultiplexing and demultiplexing unit 2 m-20 multiplexes the datagenerated by the upper layer processors 2 m-25 and 2 m-30 or the controlmessage processor 2 m-35, or demultiplexes the data received from thetransceiver 2 m-05 to transmit to the data to an appropriate upper layerprocessors 2 m-25 and 2 m-30, the control message processor 2 m-35, orthe controller 2 m-10. The control message processor 2 m-35 receives aninstruction from the controller, generates a message to be transmittedto the terminal, and delivers the generated message to a lower layer.The upper layer processors 2 m-25 and 2 m-30 may be configured for eachterminal service, processes data generated from user services such asFTP or VoIP and transfers the data to the multiplexing anddemultiplexing unit 2 m-20, or process data transmitted from themultiplexing and demultiplexing unit 2 m-20 and deliver the data to thehigher layer service application. The scheduler 2 m-15 allocatestransmission resources to the terminal at an appropriate time inconsideration of the terminal's buffer status, channel status, andterminal's active time, and processes the signal transmitted by theterminal to the transceiver or processes the signal to be transmitted tothe terminal.

In addition, the disclosure can be summarized as follows.

1. L2 header format for NR V2X

A. PDU header+m*(sub PDU header+MAC SDU)

B. PDU header=R/R/R/R/V/SRC/DST

C. Sub PDU header=R/F/LCID/L

Reference) L2 header format for LTE V2X

A. PDU header+m*sub PDU header+m*MAC SDU

B. PDU header=R/R/R/R/V/SRC/DST

C. Sub PDU header=R/E/F/LCID/L

2. L2 architecture and state variable/timer handling

A. One SLRB=PDCP entity+RLC entity

B. SLRB is identified by LCID and SRC/DST pair)

C. terminal establishes new SLRB when unknown/new LCID or unknownSRC/DST pair is indicated in the sub PDU header or PDU header

D. Timer/state variable handling (initialization)

i. T_reassembly (RLC) and T_reordering (PDCP) are set to zero

ii. RLC state variables: V2X can receive data from other terminals inthe middle

1. RX_Next_Reassembly set to the SN of the segment received first

2. RX_Next_Highest set to the SN of the segment received first

iii. PDCP state variables: V2X can receive data from other terminals inthe middle

1. RX_NEXT set to the SN of the first received PDCP PDU

2. RX_DELIV set to the SN of the first received PDCP PDU

3. Security key per service

A. Root key is identified/derived by DST ID

B. Encryption key is identified/derived by Root key, SRC ID andinformation in the PDCP header

(Different passwords can be applied for each device and message)

In Addition, the disclosure can be summarized as follows.

1. UE←V2X server: Parameter provisioning

-   -   The mapping of Destination Layer-2 ID(s) and the V2X services,        e.g. PSID, ITS-AIDs, extended sensor, platooning . . . .    -   The mapping of services to V2X frequencies/RATs (LTE or NR or        both)

2. UE interested in V2X service x: Camping on a V2X frequency of HPLMNmapped to service x

3. UE: Receiving V2X system information and determining the resourcepool for reception and resource pool for transmission

4. UE: Receiving MAC PDU in the reception pool

5. UE: L2/Security handling

-   -   For a sub-PDU        -   If SRC/DST pair of the MAC PDU is new; or        -   LCID of the sub-PDU is new        -   Create RLC and PDCP and the forward the sub PDU to the RLC            entity        -   If sub PDU contains UMD PDU segment, update the RLC state            variable accordingly        -   Update the PDCP state variable accordingly    -   If DST of the MAC PDU is new/received first time        -   Derive root key based on the DST L2 ID        -   Derive the decryption key based on the root key and SRC ID        -   Decipher the received PDCP PDU

6. UE: V2X packet to be transmitted

7. UE: L2/Security handling

-   -   If the corresponding PDCP/RLC does not exist        -   Create PDCP entity and RLC entity    -   If it is the first packet to be transmitted by the UE for a        destination/V2X service        -   Derive the root key based on the DST L2 ID        -   Derive the encryption key based on the Root key and SRC ID    -   Generate PDCP PDU and include the key id in the header    -   Encrypt the PDCP PDU data part    -   Transmit the PDCP PDU in a MAC PDU

In the above-described detailed embodiments of the disclosure, anelement included in the disclosure is expressed in the singular or theplural according to presented detailed embodiments. However, thesingular form or plural form is selected appropriately to the presentedsituation for the convenience of description, and the disclosure is notlimited by elements expressed in the singular or the plural. Therefore,either an element expressed in the plural may also include a singleelement or an element expressed in the singular may also includemultiple elements.

Although specific embodiments have been described in the detaileddescription of the disclosure, various modifications and changes may bemade thereto without departing from the scope of the disclosure.Therefore, the scope of the disclosure should not be defined as beinglimited to the embodiments, but should be defined by the appended claimsand equivalents thereof.

In the drawings in which methods of the disclosure are described, theorder of the description does not always correspond to the order inwhich steps of each method are performed, and the order relationshipbetween the steps may be changed or the steps may be performed inparallel.

Alternatively, in the drawings in which methods of the disclosure aredescribed, some elements may be omitted and only some elements may beincluded therein without departing from the essential spirit and scopeof the disclosure.

Further, in methods of the disclosure, some or all of the contents ofeach embodiment may be combined without departing from the essentialspirit and scope of the disclosure.

The invention claimed is:
 1. A method performed by a first terminal in acommunication system, the method comprising: obtaining a plurality ofsidelink medium access control (MAC) service data units (SDUs);generating a sidelink MAC protocol data unit (PDU) including a sidelinkMAC PDU header, a first sidelink MAC subheader, a first sidelink MACSDU, a second sidelink MAC subheader, and a second sidelink MAC SDU,wherein the first sidelink MAC SDU is placed in front of the secondsidelink MAC subheader and the second sidelink MAC SDU; andtransmitting, to a second terminal, the sidelink MAC PDU, wherein eachof the first sidelink MAC subheader and the second sidelink MACsubheader includes a logical channel ID (LCID) field identifying alogical channel, a length field indicating a length of a sidelink MACSDU, and a format field indicating a size of the length field, andwherein a first value of the format field indicates 8 bits of the lengthfield, and a second value of the format field indicates 16 bits of thelength field.
 2. The method of claim 1, wherein the sidelink MAC PDUheader further includes a version field indicating a version of thesidelink MAC PDU, and wherein a bit size of the version field is 4 bits.3. A method performed by a second terminal in a communication system,the method comprising: receiving, from a first terminal, a sidelinkmedium access control (MAC) protocol data unit (PDU); and identifying asidelink MAC PDU header, a first sidelink MAC subheader, a firstsidelink MAC service data unit (SDU), a second sidelink MAC subheader,and a second sidelink MAC SDU from the sidelink MAC PDU, wherein thefirst sidelink MAC SDU is placed in front of the second sidelink MACsubheader and the second sidelink MAC SDU, wherein each of the firstsidelink MAC subheader and the second sidelink MAC subheader includes alogical channel ID (LCID) field identifying a logical channel, a lengthfield indicating a length of a sidelink MAC SDU, and a format fieldindicating a size of the length field, and wherein a first value of theformat field indicates 8 bits of the length field, and a second value ofthe format field indicates 16 bits of the length field.
 4. The method ofclaim 3, wherein the sidelink MAC PDU header further includes a versionfield indicating a version of the sidelink MAC PDU, and wherein a bitsize of the version field is 4 bits.
 5. The method of claim 3, wherein astate variable for a packet data convergence protocol (PDCP) entity isset to a sequence number of a first received PDCP data PDU associatedwith the sidelink MAC PDU.
 6. A first terminal in a communicationsystem, the first terminal comprising: a transceiver; and a controllercoupled with the transceiver and configured to: obtain a plurality ofsidelink medium access control (MAC) service data units (SDUs), generatea sidelink MAC protocol data unit (PDU) including a sidelink MAC PDUheader, a first sidelink MAC subheader, a first sidelink MAC SDU, asecond sidelink MAC subheader, and a second sidelink MAC SDU, whereinthe first sidelink MAC SDU is placed in front of the second sidelink MACsubheader and the second sidelink MAC SDU, and transmit, to a secondterminal, the sidelink MAC PDU, wherein each of the first sidelink MACsubheader and the second sidelink MAC subheader includes a logicalchannel ID (LCID) field identifying a logical channel, a length fieldindicating a length of a sidelink MAC SDU, and a format field indicatinga size of the length field, and wherein a first value of the formatfield indicates 8 bits of the length field, and a second value of theformat field indicates 16 bits of the length field.
 7. The firstterminal of claim 6, wherein the sidelink MAC PDU header furtherincludes a version field indicating a version of the sidelink MAC PDU,and wherein a bit size of the version field is 4 bits.
 8. A secondterminal in a communication system, the second terminal comprising: atransceiver; and a controller coupled with the transceiver andconfigured to: receive, from a first terminal, a sidelink medium accesscontrol (MAC) protocol data unit (PDU), and identify a sidelink MAC PDUheader, a first sidelink MAC subheader, a first sidelink MAC servicedata unit (SDU), a second sidelink MAC subheader, and a second sidelinkMAC SDU from the sidelink MAC PDU, wherein the first sidelink MAC SDU isplaced in front of the second sidelink MAC subheader and the secondsidelink MAC SDU, wherein each of the first sidelink MAC subheader andthe second sidelink MAC subheader includes a logical channel ID (LCID)field identifying a logical channel, a length field indicating a lengthof a sidelink MAC SDU, and a format field indicating a size of thelength field, and wherein a first value of the format field indicates 8bits of the length field, and a second value of the format fieldindicates 16 bits of the length field.
 9. The second terminal of claim8, wherein the sidelink MAC PDU header further includes a version fieldindicating a version of the sidelink MAC PDU, and wherein a bit size ofthe version field is 4 bits.
 10. The second terminal of claim 8, whereina state variable for a packet data convergence protocol (PDCP) entity isset to a sequence number of a first received PDCP data PDU associatedwith the sidelink MAC PDU.